Multi-Method Approach in Addressing the Potential Scaling Problem for the Proposed Brine Optimization Plant at Mt. Apo Geothermal Project

Abstract

Development of a brine optimization plant is being explored in Mt. Apo Geothermal Project (MAGP), utilizing existing geothermal fluids to generate additional power without having to drill a new well. Silica fouling (scaling) is a common occurrence in a binary plant since its solubility is largely dependent on temperature, among other factors. Aside from amorphous silica, other scales have the potential to form mainly caused by brine cooling that could damage and foul the heat exchangers, pipelines and wellbores. Installment of a proper scaling inhibition system, that is thoroughly studied, will be necessary to address these potential problems. This study presents the results of a series of tests, from laboratory tests and tabletop geochemical modeling, to field tests, to simulate process conditions of the utilized brine. The two chemical methods that were investigated to inhibit silica polymerization are pH-modification using acid and silica colloidal dispersion using a chemical inhibitor. The results showed that pH-modification (lowering of pH from ~7.3 to 4.7 via acid-dosing) is the more effective method in solving the scaling problem for the MAGP binary project. The silica trends are consistent with the visual inspection and petrographic results, indicating that pH-modification is an effective solution to retard precipitation and deposition of amorphous silica inside and further downstream of the binary plant. However, corrosion risk accompanies the pH-mod method, so a robust, auto-response, acid-dosing system is needed to avoid either over-dosing or under-dosing of acid that on the other hand, can result to massive scaling.